Many techniques have been devised to increase the performance of automotive internal combustion engines. Supercharger systems have been developed that substantially boost engine performance. These systems operate to increase air pressure delivered to the intake manifold of the engine before being mixed with the fuel. The increased air pressure enhances the combustibility of the fuel, thus making it more powerful. This added power then increases engine power and torque at both lower and higher rpms than would otherwise be possible. Superchargers are simple and cheap, unlike superchargers that do not suffer from a response lag time because they are generally mechanically driven. Superchargers are more complicated and can be very expensive, although they do solve the problem of incomplete combustion when an engine is initially leaving idle speeds. Acceleration is also greatly improved with a typical mechanically driven supercharger.
However, the complicated belts and pulleys used in mechanical superchargers require for operation as much as 40% of the engine's power output, which exacts a price of shortening the engine's life span for the increased performance.
Superchargers on the other hand, are passive performance boosting devices that are driven by the exhaust from the engine. The passive design of the supercharger does not adversely affect the life span of the engine to the degree that a supercharger does.
Superchargers suffer a lag in response time because they are driven by exhaust gases and these gases are under very little pressure and velocity when the engine is at idle. The supercharger has very little rotational velocity to supply the engine with all the fresh air that is needed to complete combustion of all the fuel that is being forced into a vehicles combustion chamber. Hence large Semi's, ships, tractors, trucks, power plants and transit buses can be seen emitting black smoke as the diesel fuel is not completely burned initially on some heavy vehicles.
The superchargers have not gotten over their initial lag before they offer a power boost to the engine.
Even cars are being equipped more frequently with turbo chargers as engine size and weight must be kept to a minimum but the driving public wants more power from these smaller engines. These automobiles will suffer from the same incomplete combustion as larger vehicles although it will be less obvious from a visual point of view and surely less time in duration, but incomplete combustion none the less.
To overcome this some areas of the country are requiring oxygenated fuels, and low-sulfur diesel, be burnt in all of their vehicles especially during certain times of the year. Auto manufacturers are also to begin producing 85 compliant motors for vehicles. In essence, these vehicles can burn a mixture of 85 per cent ethanol and 15 per cent gasoline. This extra oxygen improves the initial lack of oxygen some vehicles suffer from on acceleration from low speeds or stopped conditions thereby reducing pollutants and smog contributing effects. If these engines were to be adjusted lean enough (oxygen rich-fuel stingy), for all operating conditions they would overheat during highway conditions on warm days. They can be adjusted and controlled to burn completely at cruising speeds but that leaves an oxygen-deprived state at idle.
Smaller engines in personal vehicles would be possible and acceptable to the consuming public if there were a way to supercharger these vehicles without the hassle that comes with present superchargers. This hassle is the warm-up period before a car is driven at highway speeds and a cooling-off period before the engine is shut off.
Presently, catalytic converters aid in the low emissions scenario of most gasoline powered engines, but these only work after they have become hot, and are little or no help to a cleaner burning engine when the engine is first started up, and before it is warmed up.
Another problem with ordinary superchargers is that heat of the exhaust gases which drive the supercharger is transferred to the center bearing that provides support for the supercharger's turbine. Present designs typically have an oil supply and engine coolant supply going to the supercharger bearing. This is to maintain lubrication and cooling to this critical bearing while the engine is running. This design is adequate as long as the engine is operating. However, when the engine is shut off the oil and coolant stop flowing immediately and if the bearing is supporting a hot turbine that has just been revolving at 40,000 rpm's or more the bearing literally begins to cook.
Most recommendations are for allowing the motor to idle 3 minutes before shutting off the engine. This allows this bearing to cool off before removing critical oil and cooling from the bearing. Repeated occurrences of shutting off the engine before allowing an adequate cooling-off time for the supercharger bearing leads to premature bearing failure and expensive repairs.
Several solutions have been developed to overcome the problem of turbo lag. One solution combines a supercharger with a supercharger. The supercharger drives the supercharger until the engine has reached a threshold level at which point it takes over the supercharger's job. This has the advantage of limiting the use of the supercharger, but it also has the drawback of being an active system that shortens engine life, as well as being overly complex.
By driving a simple supercharger by a belt, and keeping it simple and inexpensive, the best of both can be achieved. By removing the turbine from exhaust gas stream, the excess heating to the turbine bearing is minimized and the compressed air itself is the only factor for heating. However, this heat transfers minimally to the bearing. The bearing is thus able to better withstand possible abuse by the average driver who doesn't want to be bothered by details, such as letting the engine run for several minutes after they reach their destination.